If humans are capable of vore, this implies that vore is more casual and expected, so alien individuals who can vore are less of a threat.

If humans aren't capable, unless under special circumstances, then vore would be exclusive to aliens, and it would be implied to be more of a terrifying experience. This would basically make it a horror story.

This won't mean that vore can't have a horror vibe in the first world, or that humans can't want it in the second, but these would simply be special circumstances.